Embodiments of the present invention relate to fan speed control, and more specifically, to controlling the fan so that it is perceived as quieter.
Illustrated in FIG. 1 is a portion of a computer system comprising central processing unit (CPU) 102, chipset 104, graphics card 106, and memory 108. Chipset 104 allows for communication between CPU 102, memory 108, and graphics card 106, as well as other peripheral components (not shown) connected to system bus 110. One or more of these system components may generate an appreciable amount of heat, so that fan 112 is employed to cool part or all of the computer system. Usually, CPU 102 generates the most heat, and for some computer systems, more than one fan may be employed.
Customers of computer systems, both in the home and in business, often prefer computer systems with quiet fans. As a result, many original equipment manufacturers are sensitive to the acoustic noise generated by fans. One approach to reducing fan noise is to adjust the fan speed according to measured temperature, as shown in FIG. 1. Heat sensor 112 provides to fan voltage controller 114 a signal indicative of temperature. Heat sensor 112 may be placed near CPU 102, for example, and may be integrated with CPU 102. Fan voltage controller 114 provides a fan control voltage to fan 112 so as to adjust the speed of fan 112. When heat sensor 112 indicates that maximum cooling is needed, the fan control voltage is increased to its maximum nominal value so that fan 112 circulates sufficient air flow for cooling. When maximum cooling is not required, fan voltage controller 114 lowers the fan control voltage supplied to fan 112 so that the speed of fan 112 is reduced, along with the accompanying acoustic noise. Fan voltage controller 114 may even cause fan 112 to stand idle.
The combination of sensor 112, fan voltage controller 114, and fan 112 comprises a closed feedback loop so that the computer system of FIG. 1 is sufficiently cooled, so that the acoustic noise generated by fan 112 is reduced when CPU 102 is not operating at its maximum workload. However, the acoustic noise reduction scheme of FIG. 1 does not provide a reduction in acoustic noise when CPU 102 is operating at its maximum workload.